1. Field of the Invention
The systems and methods of this invention relate to direct electrical stimulation of brain tissue for treatment of a variety medical conditions. Specifically, the present invention relates to methods and apparatus for applying such stimulation without the use of conventional lead/electrode systems.
2. Description of the Background Art
Electrical stimulation of brain tissue is a growing treatment for many neurological disorders, including alleviation of Parkinson's and essential tremor diseases, chronic pain, depression, epileptic seizures, motor dysfunction due to stroke, and other emerging applications such as diabetes, obesity, and urinary control. Treatment regimens and targeted brain tissue locations are becoming known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for direct brain stimulation are made by such companies as Medtronic, Cyberonics, and NeuroPace.
Deep Brain Stimulation (DBS) generally refers to treatments for a variety of medical conditions that apply electrical stimulation directly on brain tissue or in regions of the brain. Currently available stimulators for DBS are battery-powered electronic devices implanted under the skin that are connected via insulated metal lead(s) to electrodes that are inserted into or onto the brain. DBS uses the inserted electrodes to deliver a variety of stimulation modalities. For example, continuous high-frequency electrical stimulation is used in areas of the brain including the thalamus, globus pallidus (GPi), or the subthalamic nucleus (STN), or other parts of the brain to control movement disorders. High frequency stimulation of cells in these areas actually shuts them down, helping to rebalance control messages throughout the movement control centers in the brain.
DBS of the thalamus is primarily used to treat disabling tremor, especially tremor that affects one side of the body substantially more than the other. Studies have shown that DBS may significantly reduce tremor in about two thirds of patients with Parkinson's disease (PD). Tremor may not be eliminated, and may continue to cause some impairment. DBS of the globus pallidus is useful in treatment of dyskinesias as well as tremor, and may improve other symptoms, as well. DBS of the subthalamic nucleus may have an effect on most of the main motor features of PD, including bradykinesia, tremor, and rigidity.
Treatment sites for movement disorders may be identified by probing brain tissue and a site predetermined for treatment is selected. As noted for movement disorders, published regions of the brain include, but are not limited to, the ventral intermediate thalamus, subthalamic nucleus, and internal globus pallidus.
Similarly, DBS has been pursued as a treatment for pain for the past 30 years. Peripheral pain signals are transmitted via the spinothalamic tract of the spinal cord and synapse primarily in the thalamus. Thus, the area where they synapse was seen as a prime target for DBS and was the focus of much of the early research. DBS continues to be pursued as a therapy in chronic pain patients. Today, the pain indications that either exist or seem most promising for potential treatment by deep brain stimulation include: neuropathic pain; Complex Regional Pain Syndrome (CRPS), Type II; steady, burning pain; lancinating, shooting pain; tactile hypersensitivity; or partial or complete sensory loss. The targets for DBS for pain typically include the following sites:
Neuropathic Pain                Medial lemniscus        Ventrobasal (VB) area of the thalamus, including the ventral posteromedial (VPM) and the ventral posterolateral (VPL) nuclei        Internal capsule        Motor cortex        Cingulate gyms (also known as cingulate cortex)        Posterior complex of the thalamus (PO)        Ventrolateral nucleus of the thalamus (VL)        
Nociceptive Pain:                Periventricular grey (PVG) matter and periaqueductal grey (PAG) matter, which are sometimes simply called periventricular grey and periaqueductal grey        
Similar targets in the brain are emerging for other DBS applications. Published targets for the treatment of depression would include, but are not limited to, one or more of the cerebellar vermis, the anterior cingulate gyrus, the dorsal prefrontal cortex, the dorsal raphe nuclei, the median raphe nuclei, and the locus coeruleus. Published targets for the treatment of epilepsy, obesity, and diabetes would include, but are not limited to, the nucleus of tractus solitarius (NTS), the sub thalamic nucleus, the hippocampus, the medial thalamus and the temporal lobe.
Upper regions of the brain, e.g., the cortex, that have been affected by stroke or injury also benefit from stimulation treatments and have been shown to be effective in rehabilitating motor performance of distal extremities. In this stroke rehabilitation treatment the electrode is placed on the dura, the membrane that covers the brain, and used to deliver stimulation to the cortex.
Currently available DBS devices are battery-powered electronic devices implanted under the skin connected via insulated metal lead(s) to electrodes which are inserted into the brain. The brain electrodes are placed into brain tissue via a small cranial hole and then connected to lead extensions which are subcutaneously tunneled between the skull and skin, down the back of the head, and around the neck to the battery-powered pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket in the pectoral region of the chest. Even in cases where the pulse generator may be located under, within, or on the skull the electrodes are still in direct connection to the pulse stimulator using a lead. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, and electrode/lead dislodgement.
There have been reported attempts to deal with the complications and limitations imposed by the use of electrical leads. For example, self-contained implantable microstimulators and remotely powered microstimulators have been described; however, each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Often, DBS devices contain rechargeable batteries due to high use or high energy requirements of the therapeutic stimulation. Implantation of the pulse generator into the skull has been proposed, which addresses the difficult procedural task of tunneling leads and avoids cosmetic appearance issues associated with the subcutaneous leads and pulse generators; however, the lead still must be placed into the brain and connected to the pulse generator.
For leadless solutions in other similar stimulation applications, remotely powered devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where stimulation must be accomplished at any significant depth (>1-2 cm) within the body, in particular where it is desired to permanently implant both the transmitter and receiver-stimulator. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced), but again relies on close proximity between transmitting and receiving coils, or the utilization of relatively large devices for deeper (5-8 cm maximum) implantation.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for DBS, by achieving a brain stimulation capability without the use of leads connected to a stimulation controller/pulse generator.
The following patents, all of which are incorporated in this disclosure in their entirety, describe various aspects of using electrical stimulation for achieving various beneficial effects. U.S. Pat. No. 5,716,377 titled “Method of Treating Movement Disorders by Brain Stimulation” by Rise et al. describes a typical implantable DBS system for treating movement disorders such as Parkinson's. U.S. Pat. No. 7,013,177 titled “Treatment of Pain by Brain Stimulation” by Whitehurst et al. describes an implantable DBS system that uses electrical stimulation in the form of a microstimulator in combination with drug delivery for the treatment of pain. U.S. Pat. No. 5,405,367 titled “Structure and Method of Manufacture of an Implantable Microstimulator” by Schulman et al. describes an implantable microstimulator used generally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled “Ultrasonic Power Communication System” by Welle describes the use of ultrasound energy transfer from a transmitter to a receiver for purposes of powering a sensor or actuator without being connected by a lead/wire. U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment with Wireless Satellite Units” by Marchesi describes a tissue stimulation system based on a wireless radio transmission requiring the charging of a battery at the receiver and separate command signals used to control the delivery of stimulation. German patent application DE4330680A1 titled “Device for Electrical Stimulation of Cells within a Living Human or Animal” by Zwicker describes a general approach to power transfer using acoustic energy for tissue stimulation. U.S. Pat. No. 7,010,351 titled “Methods and apparatus for effectuating a lasting change in a neural-function of a patient” by Firlik et al. describes a DBS system used to treat or effectuate changes to neural function particularly by stimulation in the region of the cortex. U.S. Pat. No. 6,427,086 titled “Means and method for the intracranial placement of a neurostimulator” by Fischell et al. describes a DBS device implanted in the skull. U.S. Pat. No. 6,016,449 titled “System for treatment of neurological disorders” by Fischell et al. describes the use of a DBS device for the treatment of epilepsy. U.S. Pat. No. 5,782,798 titled “Techniques for treating eating disorders by brain stimulation and drug infusion” by Rise describes a DBS system for treating eating disorders with electrical stimulation in regions of the brain.